Material deposited: Host symbiotype in the Colorado
State University Mammal
Collections # 10184 (Vetterling, 1964). There is a suitable drawing (Figure 1) in
Vetterling (1964) and a suitable photomicrograph (Figure 3) in Dorney
(1965).

Etymology: The trivial name is derived from gigas-
(Gk, a giant) and os,
because Dorney (1965) originally named the form he saw as E. os.

Remarks: Vetterling (1964) found oocysts similar
in size to those of E. cynomysis
(30-37 x 25-31 [Vetterling, 1964] vs. 25-37 x 22-32 [Andrews, 1928]) and, thus,
emended the original description. However, Vetterling's (1964) oocysts were
smooth-walled and had a prominent SB while those of Andrews (1928) were rough-walled
with an inconspicuous SB. Thus, we renamed those of Vetterling (1964) to E.
giganteos. Dorney (1965) described and photographed what he called E. os
from M.
monax, but the sporulated oocysts he described were so much larger (34-37 x
23-26)
than those of E. os (20-26 x 18-22) of Crouch & Becker (1931), that we
believe the
form Dorney saw was E. giganteos not E. os. The sporocysts measured
by Dorney (1965)
also were proportionally smaller than those of Crouch & Becker (1931) to further
support our decision to separate these species. Nukerbaeva & Abenov (1979) described
a species from M. bobak they called E. marmotae, (described by
Galli-Valerio [1923],
but designated a species inquirenda by us because the description was based
on
unsporulated oocysts). The few descriptive characters (by Nukerbaeva and Abenov,
1979) are indistinguishable from the description by Vetterling (1964) for E.
cynomysis (now E. giganteos). Fleming et al. (1979) and McQuistion &
Wright (1984)
reported E. os from M. monax. However, they followed Dorney (1965);
therefore, it is
likely they all actually saw E. giganteos.